Conduction Q. for sleeping bags

10:55 a.m. on April 18, 2009 (EDT)
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With conduction(to the ground) being the largest heat loss after convection(to the air), would a synthetic sleeping bag be better suited than a down in wet and or temps around 0c?

While in the shop I seen a synthetic rated to -5c and a down to -5c, the synthetic was of course heavier and bulkier, but I am assuming the synthetic would insulate me better from the ground as it would compress less and there is more of it(filling) and so in turn be warmer!

I put one hand inside the down bag and put another under the bag, I could almost feel my finger through it, felt like no filling was there, where as the synthetic because it has double the weight of filling felt soft like a pillow, this must make a difference as under your weight there would be no loft.

Would this be the case?

Down bag 850g(weight) 450g filling rated to -5

Syn bag 1500g(weight) 850g filling rated to -5

Both will be used on a high quality mat of course

Going to make an expensive purchase, want to make the right one!

Thanks for any feedback!

11:35 a.m. on April 18, 2009 (EDT)
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You asked if a synthetic would be better suited for "wet and or temps around 0". For wet, the answer is synthetic. For low temps, one is not really any better than the other, as long as you know that the synthetic will probably be heavier.

As far as insulation, it sounds to me like your logic is sound, but the real question is how much of a difference it will make. Trapping air is how insulation keeps you warm, and even a synthetic isn't going to trap much air when you're laying on it.

I think you're right, though... it would be warmer than down while you were laying on it.

1:21 p.m. on April 18, 2009 (EDT)
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The big question: is the extra weight of a synthetic bag really is warmer than adding another foam pad under you? You can always use an hybrid bag with down upper and synthetic bottom, available from a few manufacturers, including MEC

I'd rather add a foam pad or a self-inflater than rely on the sleeping bag for ground insulation. Actually, i never zip my bag and sleep straight on my pad, even in sub-zero weather.

9:31 p.m. on April 18, 2009 (EDT)
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The reality is that both synthetic and down bags provide effectively no insulation between you and the ground without a mat. With a sleeping pad (whether closed cell or inflatable), all the insulation from the ground is provided by the pad, with the possible exception of some really cheap quality synthetic fills that have essentially no compression (like Quallofil). This comes not only from studies made by bag manufacturers (ones making both types of fills, so no ax to grind there), but also my personal experience (I used to have two similar bags from the same manufacturer, one with Polargard, the other with the highest quality down available at the time, both rated to -10F - a group of us were headed into the Sierra for a snowshoe trip, drove up to Kings Canyon the night before and just tossed our sleeping bags out at the edge of the parking lot, without bothering to get the pads out. I had the Polargard bag for that trip. We were cold enough that by 2AM, most of us had decided to unpack the pads, and then slept warmly the rest of the night).

July 29, 2014
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